This is the final phase of a multivariate young adult follow-up study of several samples of boys with the Hyperkinetic/Attention Deficit Disorder (HK/ADD), of their nonhyperkinetic full brothers, and of nonhyperkinetic volunteer classmates. All patients were originally evaluated at ages 6 to 12 as referrals to the University of Iowa child psychiatry clinic; all were diagnosed as HK/ADD by child psychiatry faculty/residents; all were treated either pharmacologically (primarily with methylphenidate) of psychologically (primarily with short-term parent and/or teacher counseling); and all are being followed up by the present investigator at adolescence (ages 12-18) and/or young adulthood (ages 21-23). The samples are: a) an Early Medicated group (HK/ADD boys diagnosed between 1967-1972 and treated with methylphenidate for an average of 3 years); b) a Transitional Medicated group (HK/ADD boys diagnosed between 1972-1975 and also treated with methylphenidate); c) a Transitional Unmedicated group HK/ADD boys also diagnosed between 1972-1975 but not treated with psychotropic drugs); and d) a Late Unmedicated group (HK/ADD boys diagnosed between 1975-1978 and not treated with psychotropic drugs). A total of 179 Early Medicated patients, 37 Transitional Medicated patients, 19 Transitional Unmedicated patients, 25 Late Unmedicated patients, 136 brothers, and 46 classmates will have been seen within two years after their 21st birthday and administered a multitrait and multimethod battery of tests, questionnaires, and interviews. The general aim of the present study is to describe the life course of the HK/ADD child and to identify the individual predictors (e.g., aggression, IQ) and the environmental predictors (e.g., treatment, parenting styles) of differences in life course. Results of a series of multivariate analyses will provide a detailed description of a variety of outcomes among both medicated and unmedicated HK/ADD boys as adolescents and young adults, with classmate and sibling controls. Planned comparisons will test the effects on outcomes of hyperkinesis per se; of stimulant drug treatment; and of response to medication. Establishing means for predicting and diagnosing residual ADD/adult MBD will be a special concern of this investigation.